To understand how the vertebrate visual system functions, we need to know how its components are wired into an integrated functional network. The eye, a highly ordered arrangement of receptors and interneurons, is connected in precise order to several different visual neuropils, which are, themselves wired to one another. Such networks are produced, in part, as a result of genetic programming of visual center maturation, optic fiber outgrowth, pathway development and the formation of ordered connections. We would like to understand the programming rules that govern these processes during visual system development in the frog, Xenopus. This organism lends itself to a wide variety of embryological procedures that specifically modify visual system development. Their effect on optic fiber pathways and connections can be studied by several anatomical procedures (EM, HRP tracing, proline autoradiography, cobalt filling, fluorescent labeling, ect.) and correlated with physiological recording of visuotectal maps. For the past few years we have been studying normal development and regeneration of retina, optic nerve and tract as well as visual neuropil maturation, first to establish a normative baseline and secondly to identify those morphogenetic factors that are responsible for ordering connections. Such factors as asymmetry and timing of retinal maturation and fiber outgrowth combined with the phenomenon of fiber following are being tested within a broad framework of a space time model for ordering connectivity.